GM Service Manual Online
For 1990-2009 cars only

NORMAL Inhibits Which Result in a Blinking PRNDL

High engine speed NEUTRAL to Range shifts : When a NEUTRAL to DRIVE or NEUTRAL to REVERSE shift is made, when engine RPM is high, the shift is inhibited to NEUTRAL. The TCM has torque management capability and attempts to slow the engine to a point where it makes the requested shift.

High Throttle or Torque Direction Change Shifts:  REVERSE to DRIVE, DRIVE to REVERSE, NEUTRAL to DRIVE, and NEUTRAL to REVERSE shifts, where throttle position is greater than 25 percent, are inhibited to NEUTRAL. The TCM has torque management capability and attempts to slow the engine to a point where it makes the requested shift.

Four-Wheel Drive Transfer Case in NEUTRAL:  If the four-wheel drive transfer case is shifted into NEUTRAL while the transmission is in DRIVE or REVERSE, the transmission continues to the commanded range until output speed is low, at which point NEUTRAL is commanded. If the driver attempts to shift the transmission from NEUTRAL to DRIVE or NEUTRAL to REVERSE, with the transfer case in NEUTRAL, the PRNDL display blinks immediately.

High Output Speed Direction Change Shifts : REVERSE to DRIVE, DRIVE to REVERSE, and NEUTRAL to REVERSE shifts, initiated above 300 RPM output speed are inhibited to NEUTRAL.

Low Automatic Transmission Fluid (ATF) Level Low: Low ATF level is caused by insufficient transmission fluid and lack of initial pump prime, caused by refilling the transmission.

Extremely Low ATF temperature: A shift out of NEUTRAL when the ATF temperature is below -45°C (-49°F) may be inhibited.

MALFUNCTIONS Which May Cause a Blinking PRNDL

Failure to detect turbine speed pull-down during a shift may occur under the following conditions:

    • A clutch is failed and the transmission cannot attain the requested range.
    • Invalid gear ratio
    • Pressure control solenoid failure
    • Turbine or output speed sensor failure
    • Lack of pressure at startup

Conditions Which May Cause a BLANK PRNDL

The PRNDL display may be blank because of failure of the internal mode switch circuits A, B, C, or P.

The transmission will command the most appropriate range, based on reverse pressure switch and the remaining internal mode switch inputs.